The present invention relates to liquid transport members useful for a wide range of applications requiring high flow and/or flux rate, wherein the liquid can be transported through such a member, and/or be transported into or out of such a member. Such members are suitable for many applications, asxe2x80x94without being limited toxe2x80x94water irrigation systems, spill absorbers, oil/water separators and the like. The invention further relates to liquid transport systems comprising said liquid transport members and articles utilizing these.
The need to transport liquids from one location to another is a well known problem.
Generally, the transport will happen from a liquid source through a liquid transport member to a liquid sink, for example from a reservoir through a pipe to another reservoir. There can be differences in potential energy between the reservoirs (such as hydrostatic height) and there can be frictional energy losses within the transport system, such as within the transport member, in particular if the transport member is of significant length relative to the diameter thereof.
For this general problem of liquid transport, there exist many approaches to create a pressure differential to overcome such energy differences or losses so as to cause the liquids to flow. A widely used principle is the use of mechanical energy such as pumps. Often however, it will be desirable to overcome such energy losses or differences without the use of pumps, such as by exploiting hydrostatic height differential (gravity driven flow), or via capillary effects (often referred to as wicking).
In many of such applications, it is desirable to transport the liquids at high rates, i.e. high flow rate (volume per time), or high flux rate (volume per time per unit area of cross-section).
Examples for applications of liquid transport elements or members can be found in fields like water irrigation such as described in EP-A-0.439.890, or in the hygiene field, such as for absorbent articles like baby diapers both of the pull-on type or with fastening elements like tapes, training pants, adult incontinence products, feminine protection devices.
A well known and widely used execution of such liquid transport members are capillary flow members, such as fibrous materials like blotting paper, wherein the liquid can wick against the gravity. Typically such materials are limited in their flow and/or flux rates, especially when wicking height is added as an additional requirement. An improvement particularly towards high flux rates at wicking heights particularly useful for example for application in absorbent articles has been described in EP-A-0.810.078.
Other capillary flow members can be non-fibrous, but yet porous structures, such as open celled foams. In particular for handling aqueous liquid, hydrophilic polymeric foams have been described, and especially hydrophilic open celled foams made by the so called High Internal Phase Emulsion (HIPE) polymerization process have been described in U.S. Pat. Nos. 5,563,179 and 5,387,207.
However, in spite of various improvements made on such executions, there is still a need to get significant increase in the liquid transport properties of liquid transport members.
In particular, it would be desired to obtain liquid transport members, that can transport liquid against gravity at very high flux rates.
In situations wherein the liquid is not homogeneous in composition (such as a solution of salt in water), or in its phases (such as a liquid/solid suspension), it can be desired to transport the liquid in its totality, or only parts thereof. Many approaches are well known for their selective transport mechanism, such as in the filter technology.
For example, filtration technology exploits the higher and lower permeability of a member for one material or phase compared to another material or phase. There is abundance of art in this field, in particular also relating to the so called micro-, ultra-, or nano-filtration. Some of the more recent publications are:
U.S. Pat. No. 5,733,581 relating to melt-blown fibrous filter;
U.S. Pat. No. 5,728,292 relates to non-woven fuel filter;
WO-A-97/47375 relating to membrane filter systems;
WO-A-97/35656 relating to membrane filter systems;
EP-A-0.780.148 relating to monolithic membrane structures;
EP-A-0.773.058 relating to oleophilic filter structures.
Such membranes are also disclosed to be used in absorbent systems.
In U.S. Pat. No. 4,820,293 (Kamme) absorbent bodies are disclosed, for being used in compresses, or bandages, having a fluid absorbent substance enclosed in a jacket made of one essentially homogeneous material. Fluid can enter the body through any part of the jacket, and no means is foreseen for liquid to leave the body.
Therein, fluid absorbent materials can have osmotic effects, or can be gel-forming absorbent substances enclosed in semipermeable membranes, such as cellulose, regenerated cellulose, cellulose nitrate, cellulose acetate, cellulose acetate butyrate, polycarbonate, polyamide, fiberglass, polysulfone, of polytetrafluoroethylene, having pore sizes of between 0.001 xcexcm and 20 xcexcm, preferably between 0.005 xcexcm and 8 xcexcm, especially about 0.01 xcexcm.
In such a system, the permeability of the membrane is intended to be such that the absorbed liquid can penetrate, but such that the absorbent material is retained.
It is therefore desired to use membranes having a high permeability k and a low thickness d, so as to achieve a high liquid conductivity k/d of the layer, as being described herein after.
This can be achieved by incorporation of promoters with higher molecular weight (e.g., polyvinyl pyrrolidone with a molecular weight of 40,000), such that the membranes can have larger pores leading to larger membrane permeability k. The maximum pore size stated therein to be useful for this application is less than 0.5 xcexcm, with pore sizes of about 0.01 xcexcm or less being preferred. The exemplified materials allow the calculation of k/d values in the range of 3 to 7*10xe2x88x9214 m.
As this system is quite slow, the absorbent body can further comprise for rapid discharge of fluids a liquid acquisition means, such as conventional acquisition means to provide interim storage of the fluids before these are slowly absorbed.
A further application of membranes in absorbent packets is disclosed in U.S. Pat. No. 5,082,723, EP-A-0.365.565, or U.S. Pat. No. 5,108,383 (White; Allied-Signal).
Therein, an osmotic promoter, namely a high-ionic strength material such as NaCl, or other high osmolality material like glucose or sucrose is placed inside a membrane such as made from cellulosic films. As with the above disclosure, fluid can enter the body through any part of the jacket, and no means is foreseen for liquid to leave the body. When these packets are contacted by aqueous liquids, such as urine, the promoter materials provide an osmotic driving force to pull the liquid through the membranes. The membranes are characterized by having a low permeability for the promoter, and the packets achieve typical rates of 0.001 ml/cm2/min. When calculating membrane conductivity k/d values for the membranes disclosed therein, values of about 1 to 2* 10xe2x88x9215 m result. An essential property of membranes useful for such applications is their xe2x80x9csalt retentionxe2x80x9d, i.e. whilst the membranes should be readily penetrable by the liquid, they must retain a substantial amount of the promoter material within the packets. This salt retention requirements provides a limitation in pre size which will limit liquid flux.
U.S. Pat. No. 5,082,723 (Gross et al.) discloses an osmotic material like NaCl which is enclosed by superabsorbent material, such as a copolymer of acrylic acid and sodium acrylate, thereby aiming at improving absorbency, such as enhanced absorptive capacity on a xe2x80x9cgram per gramxe2x80x9d basis and absorption rate.
Overall, such fluid handling members are used for improved absorbency of liquids, but have only very limited fluid transport capability.
Thus, there remains still a need to improve the liquid transport properties, in particular to increase the flow and/or flux rates in liquid transport systems.
The present invention is a liquid transport member comprising at least one bulk region and a wall region that completely circumscribes the bulk region, whereby the wall region further comprises at least one membrane port region and at least one open port region, and whereby the bulk region has an average fluid permeability kb which is higher than the average fluid permeability kp of the membrane port region. Preferably, the bulk region has a fluid permeability of at least 10xe2x88x9211 m2, or at least 10xe2x88x928 m2, more preferably of at least 10xe2x88x927 m2, most preferably of at least 10xe2x88x925 m2. The membrane port region has preferably a fluid permeability of at least 6*10xe2x88x9220 m2, or at least 7*10xe2x88x9218 m2, more preferably of at least 3*10xe2x88x9214 m2, even more preferably of at least 1.2*10xe2x88x9211 m2, and even at least 7*10xe2x88x9211 m2, most preferably of at least 10xe2x88x929 m2.
A liquid transport member according to the present invention further can have for the membrane port region a ratio of fluid permeability to thickness in the direction of fluid transport, kp/dp of at least 3*10xe2x88x9215 m, preferably of at least 7*10xe2x88x9214 m, more preferably of at least 3*10xe2x88x9210 m, even more preferred of at least 8*10xe2x88x928 m, and even preferred of at least 5*10xe2x88x927 m, and most preferred of at least 10xe2x88x925 m.
In a particular arrangement the liquid transport member according to the present invention is positioned such that the membrane port region is arranged above said open port region when positioned for its intended use.
In a further embodiment, a liquid transport member according to the present invention the open port region is an opening having a inner circular diameter of less than the corresponding diameter db of a gas bubble formed in the liquid within the bulk region, or of less than 6 mm, preferably less 4 mm, more preferably less than 2 mm.
In another aspect of the present invention, a liquid transport member can have a ratio of permeability of the bulk region to the permeability of the membrane port region of at least 10, preferably at least 100, more preferably at least 1000, and even more preferably at least 10000.
In yet another aspect, a liquid transport member according to the present invention, the membrane port region has a bubble point pressure as measured with a liquid having a surface tension value of 72 mN/m of at least 1 kPa, preferably at least 2 kPa, more preferably at least 4.5 kPa, even more preferably 8 kPa, most preferably 50 kPa, or has a bubble point pressure as measured with a liquid having a surface tension value of 33 mN/m of at least 0.67 kPa, preferably at least 1.3 kPa, more preferably at least 3.0 kPa, even more preferably 5.3 kPa, most preferably 33 kPa.
A liquid transport member according to the present invention can have a bulk region which has a larger average pore size than membrane port region, preferably such that the ratio of average pore size of the bulk region and the average pore size of the membrane port region is at least 10, preferably at least 50, more preferably at least 100, and even more preferably at least 500, and most preferably at least 1000. The liquid transport member can have a bulk region with an average pore size of at least 200 xcexcm, preferably at least 500 xcexcm, more preferably of at least 1000 xcexcm, and most preferably of at least 5000 xcexcm, or with a porosity of at least 50%, preferably at least 80%, more preferably at least 90%, even more preferably of at least 98%, and most preferably of at least 99%.
In a particular design, a liquid transport member according to the present invention can be constructed by a bulk region, which is a void circumscribed by a wall region.
In a further aspects of the present invention, a liquid transport member can have a membrane port region with a porosity of at least 10%, preferably at least 20%, more preferably of at least 30%, and most preferably of at least 50%, or an average pore size of no more than 100 xcexcm, preferably no more than 50 xcexcm, more preferably of no more than 10 xcexcm, and most preferably of no more than 5 xcexcm. In another aspect, the membrane port region has a pore size of at least 1 xcexcm, preferably at least 3 xcexcm. Further, the membrane port region can have an average thickness of no more than 100 xcexcm, preferably no more than 50 xcexcm, more preferably of no more than 10 xcexcm, and most preferably of no more than 5 xcexcm.
In yet another aspect of the present invention, a liquid transport member can have a bulk region and a wall region having a volume ratio of at least 10, preferably at least 100, more preferably at least 1000, and even more preferably at least 10000.
In a further aspect of the present invention, a liquid transport member has a hydrophilic membrane port region, preferably by having a contact angle for the liquid to be transported less than 70 degrees, preferably less than 50 degrees, more preferably less than 20 degrees, and even more preferably less than 10 degrees. In a particular aspect, the membrane port region does not substantially decrease the liquid surface tension of the liquid that is to be transported.
In another embodiment of the present invention, a liquid transport member has an oleophilic membrane port region, preferably by having a contact angle for the liquid to be transported less than 70 degrees, preferably less than 50 degrees, more preferably less than 20 degrees, and even more preferably less than 10 degrees.
In particular embodiments, the shape of the liquid transport member can be sheet-like shape, or has a cylindrical like shape, and the membrane port region can have a larger area than the average cross-section of the member along the direction of liquid transport, preferably by at least a factor of 2, preferably a factor of 10, most preferably a factor of 100.
The liquid transport member according to the present invention can comprise a material which is expandable upon liquid contact and collapsible upon liquid removal.
In particular, the bulk region of a liquid transport member according to the present invention can comprise a material selected from the groups of fibers, particulates, foams, spirals, films, corrugated sheets, or tubes, and the wall region can comprise a material selected from the groups of fibers, particulates, foams, spirals, films, corrugated sheets, tubes, woven webs, woven fiber meshes, apertured films, or monolithic films. The foam for such embodiments can be an open cell reticulated foam, preferably selected from the group of cellulose sponge, polyurethane foam, HIPE foams, and the fibers can be made of polyolefins, polyesters, polyamids, polyethers, polyacrylics, polyurethanes, metal, glass, cellulose, cellulose derivatives.
A liquid transport member according to the present invention can be made by a porous bulk region that is wrapped by a separate wall region.
In a further embodiment of the present invention, a liquid transport member can comprise water soluble materials, such as in the port regions.
A liquid transport member according to the present invention can be adopted for the transport of water-based liquids or of viscoelastic liquids, or for the transport of oil, grease, or other non-water based liquids. Thereby, the transport can be selective for oil or grease, but not water based liquids.
In another aspect, the liquid transport member according to the present inventions, properties or parameter of the member are established prior to or at the liquid handling, preferably by activation by contact with the liquid, pH, temperature, enzymes, chemical reaction, salt concentration or mechanical activation.
In yet another aspect, the present invention relates to a liquid transport system comprising a liquid transport member as described before, and further a source of liquid and a sink of liquid that are outside the liquid transport member. In a particular aspect, the open port region is immersed in the liquid of sink or source.
A liquid transport system according to the present invention is particularly suitable for the absorption of liquids, such as having an absorption capacity of at least 5 g/g, preferably at least 10 g/g, more preferably at least 50 g/g when submitted to the Demand Absorbency Test, or by comprising sink material, that has an absorption capacity of at least 10 g/g, preferably at least 20 g/g and more preferably at least 50 g/g on the basis of the weight of the sink material, when submitted to the Teabag Centrifuge Capacity. The liquid transport system can comprise superabsorbent material or open celled foam of the High Internal Phase Emulsion (HIPE) type. Optionally, a liquid transport system can further comprise a conventional mechanical pump.
A further aspect of the present invention relates to an article comprising a liquid transport member or a liquid transport system as described before. Such an article can be suitable as a grease absorber, or as a water transport member.